UPDATE 4.20PM: Heavy traffic conditions and delays are still being felt northbound on the Princes Highway at Batemans Bay and southbound at Oak Flats.

UPDATE 3.25pm: The Princes Highway and Moss Vale Road have both reopened following earlier incidents, but heavy holiday traffic is still causing some headaches.

Significant delays are still being experienced southbound on the Princes Highway near Lake Entrance Road despite a car accident there being cleared.

Drivers on Moss Vale Road are being urged to exercise caution following a landslide and a fallen tree that closed the road for several hours earlier today.Motorists can also expect heavy traffic northbound on the Princes Highway around Batemans Bay and also on Jervis Bay Rd at Vincentia.

UPDATE 1.30pm: Traffic is building on the Princes Highway due to a collision and the rain.

At Oak Flats, at the intersection of Lake Entrance Road and the Princes Highway, a car has rolled causing traffic to back up in southbound lanes.

Holiday traffic heading home from the South Coast has also slowed northbound as drivers observe the scene.

Lake Illawarra police say no one was injured in the accident.

Traffic is also building in Albion Park as heavy rain reduces visibility.

There are no reports of flooding yet however, police advise Swamp Road Dunmore is likely to close this afternoon.

Meantime, Moss Vale Road at Kangaroo Valley is currently closed in both directions due to a fallen tree and an earlier landslide.

Police are on scene diverting traffic, with motorists advised to avoid the area and use the Illawarra or Kings Highway as an alternative route.

Police fear that heavy weather conditions will make today’s holiday traffic much worse and are urging motorists to be cautious.

Today is expected to be one of the busiest on the roads, coming at the end of the Australia Day long weekend, as well as the end of the summer holidays.

Police are advising people to stay off the road, reconsider their travel plans and even delay their trips where possible.

Those motorists who do set out are advised to check on weather conditions and road closures before driving.

NSW SES Commissioner Murray Kear said drivers needed to exercise patience, drive to the conditions and never enter flood water.

"If you need emergency help in a flood or storm call the NSW SES on 132 500. If your situation is life-threatening call triple-0," he said.

Weather conditions are expected to worsen this afternoon with heavy rain and gale-force winds.